1) Technical Field of the Invention
The present invention relates to a printed-circuit board for receiving a semiconductor integrated circuit (IC) mounted thereon, and a semiconductor module including the semiconductor integrated circuit, and as well as to a manufacturing process of the semiconductor module.
2) Description of the Related Art
In the case where the IC having a plurality of pins provided with a ball-like solder or a solder bump is mounted on a circuit substrate using a packaging technology such as BGA (ball grid array) and CSP (chip scale package), the circuit substrate made of, for example, epoxy resin is provided with a plurality of isolated lands, each of which is aligned and connected, one to one correspondence, to the ball-like solder. The land, which is preformed of a film layer of, for instance, copper deposited on the circuit substrate is rounded so that it corresponds to the ball-like solder bump.
FIG. 10 shows a cross sectional view of the conventional semiconductor module receiving the IC with ball-like solders on the circuit substrate. In this drawing, the circuit substrate 1 supports a plurality of lands 2, each connected with associated wire 3. Both lands 2 and wires 3 are printed on the circuit substrate 1. The lands 2 are arrayed on the circuit substrate 1 corresponding, in number and in shape, to the ball-like solders provided on the opposing surface, i.e. the lower surface in the drawing, of the Integrated Circuit (IC) 4. Also, a protection layer 6 made of photoresist is provided on the wires 3, but not on the lands 3 to allow the lands 3 connected with ball-like solders on the IC 4.
For better understanding the problems to be solved by the present invention, FIG. 10 also shows not only ball-like solders properly fused but also that improperly fused, which are designated by numerals 5a and 5b, respectively. As shown, the properly fused ball-like solder 5a is completely soldered and thereby extends across the entire surface of the land 3. Meanwhile the improperly fused ball-like solder 5b is not completely soldered at its portion facing to the land 3, leaving a space gap extending around the land 3 between the land 3 and the fused ball-like solder 5b. 
The improper soldering may bring a mal-function such as open circuit, significantly reducing the reliability of the semiconductor module 8. Thus, after soldering, a test should be made to determine whether the soldering has been performed properly. However, since a plenty of ball-like solders 5 are provided two-dimensionally between the IC 4 and the circuit substrate 1, it is difficult to determine the quality of the soldering by the visual inspection from the peripheral edge of the semiconductor module 8. Therefore, many processes for determining the quality of the soldering have been developed including a fluoroscopic test in which X-rays is illuminated from above the IC 4 to image the configuration of the fused balls, determining whether ball-like solders 5 have been properly soldered.
FIG. 11 shows, in part, a photofluorographic image of the semiconductor module 8, viewed from above thereof with a soft X-rays. As shown in an exaggerated fashion, the ball-like solders 5 can be seen more clearly due to the reduced transmissivity thereof than others, as a cross-hatched portion, which are darker than the other portions (thus, the hatching is used only for exaggeration but not for indication of a cross-section.
However, where the module 8 is designed so that the ball-like solders 5 and the lands 2 on the circuit substrate 1 have substantially the same diameter, the images of the properly fused ball-like solders 5a can be hardly distinguished from those of the improperly fused ball-like solders 5b even by the fluoroscopic test from above thereof, because both images look same configurations as shown in FIG. 11.
To solve this problem, the prior arts, such as JP-A 9-51017, and JP-A 11-4067 disclose the lands 2 designed such that they have the diameter greater than, or the configuration different from those of the ball-like solders 5.
This technique causes the reproduced image to show the configuration of the fused ball-like solders, allowing to readily judge whether the ball-like solders are properly soldered.
Disadvantageously, this requires a larger area of the lands 5 on the circuit substrate 1 therefor, which provides a great restriction in patterning the wires 3 on the circuit substrate 1. Also the larger lands 5 provides another restriction in reducing the intervals of the adjacent ball-like solders 5 in accordance with the miniaturization of IC 4 and the increase of pins, which are normally required in the highly integrated circuit.
Therefore, the present invention was made to solve the problems as aforementioned above, and the first purpose thereof is to provide a printed-circuit board, which can be easily inspected to determine the quality of the soldering when the IC with the ball-like solder of BGA, CSP or the like, is mounted on the circuit substrate, while allowing the high density mounting, even in the case where each land has approximately the same area as the ball-like solder.
Also, the second purpose of the present invention is to provide a semiconductor module which can be easily inspected to determine the quality of the soldering when the IC with the ball-like solders of BGA or CSP etc., is mounted on the circuit substrate, while allowing the high reliability and the high density mounting.
Further, the third purpose of the present invention is to provide a manufacturing process of the semiconductor module which can be easily inspected to determine the quality of the soldering when the IC with the ball-like solder of BGA, CSP or the like, is mounted on the circuit substrate, while allowing the high reliability and the high density mounting.
According to a printed-circuit board of the present invention, it comprises, a circuit substrate; a plurality of patterned wires formed on a surface of said circuit substrate; a plurality of lands, each land connected to at least one of said patterned wires through an end portion thereof; and a protection layer with a plurality of openings, covering the surface of said circuit substrate, wherein said land and said end portion connected thereto are exposed in the associated opening of said protection layer.
Also according to the printed-circuit board of the present invention, each of the end portions of said patterned wires is tapered away from one of said lands connected thereto.
According to a semiconductor module of the present invention, it comprises, a printed-circuit board, including a circuit substrate, a plurality of patterned wires formed on a surface of said circuit substrate, a plurality of lands, each land connected to at least one of said patterned wires through an end portion thereof; a semiconductor integrated circuit having a plurality of pins; and a plurality of ball-like solders formed on each of said pins to mount said semiconductor integrated circuit upon said printed-circuit board such that each of said ball-like solders is fused onto one of said lands and on the end portion of said patterned wires connected thereto.
Also according to the semiconductor module of the present invention, the printed-circuit board further including a protection layer with a plurality of openings, covering the surface of said circuit substrate; wherein each of said lands and end portions are exposed in the associated opening of said protection layer.
Further, according to the semiconductor module of the present invention, wherein each of the end portions of said patterned wires is tapered away from one of said lands connected thereto.
According to a process for manufacturing the semiconductor module of the present invention, which comprises steps of: covering an entire surface of a circuit substrate with a protection layer, wherein a plurality of patterned wires and lands are formed on said circuit substrate such that each of said patterned wires are connected at least one of said lands through an end portion thereof; opening a plurality of openings within said protection layer, each of said lands and end portions being exposed therethrough; aligning and connecting ball-like solders of a semiconductor integrated circuit to said lands; fusing said ball-like solders onto said lands and end portions of said patterned wires connected thereto, by heating the semiconductor module; and inspecting a shape of soldering by fluoroscoping the semiconductor module with a X-rays.
Also, according to the process for manufacturing the semiconductor module of the present invention, it further comprises steps of, removing said protection layer out after fusing said ball-like solders.